Pulley

Abstract: Pulley, in particular for a continuously variable transmission, provided with at least two discs (21,22,23,24), which are installed on a pulley shaft (25,26) and are fixed against mutual rotation and wherein at least one of the discs (22,23) is installed so as to be axially slidable in relation to the shaft (25,26). The pulley is provided with compensation means (49,50) which exert a resultant eccentric, axially-directed force between the discs.

Description: The invention relates to a pulley in particular for a continuously variable transmission, provided with at least two discs, which are primarily co-axially installed on a pulley shaft and are fixed against mutual rotation, wherein at least one of the discs is slidable in relation to the shaft by means of displacement means and wherein compensation means are provided to exert a resultant eccentric, axially-directed force between the discs. Such a pulley is known from WO-A-90/01129. Said known pulley, in particular the compensation means thereof, is rather cumbersome which makes it less suitable for applications wherein the available space is limited. The object of the invention is to further develop such a pulley. This object is achieved in that at least that part of the shaft lying between the point of application of the resultant force to be exerted by the compensation means and that disc that is nearest to said compensation means are made primarily relatively flexible. An optimal compensation effect can be realized in case the relatively flexible part of the shaft is thinner than the basic shaft. The slidable disc is preferably at least partially mounted onto the relatively flexible part of the shaft. According to another feature of the invention, a disc is supported on the shaft by means of a hinge, preferably a ball hinge, to support the operation of the compensation means. The fixed disc and the shaft can be advantageously rigidly mounted by providing the part of the shaft adjacent to the side of the slidable disc which is furthest away from the fixed disc, with at least two bearings. The first and the second bearings can be connected by a securable torsion-rigid bearing housing. According to the invention, the compensation means can be equipped to exert a variable resultant eccentric axially-directed force, The first bearing at the location of the fixed disc, possibly surrounded by the fixed disc, and a second bearing at a distance from the fixed disc. Because of this, the resultant force can be adjusted depending on the desired contact pressure and/or the desired point of application. According to a further elaboration of the invention, the compensation means comprise a power cylinder. By connecting the power cylinder to an operating cylinder of a moveable disc, the following is realized: the prevailing pressure in the power cylinder is the same as, or is a derivative from, the transmission ratio-dependent pressure in the operating cylinder, which is also a measure for the (ec)centric load of a disc. The power cylinder can also be connected to the operating cylinder in an advantageous way by means of a control system. According to the invention, the power cylinder can operate on a shaft bearing, preferably at some distance from a disc. The assembly can therefore be simply built into a transmission. Moreover, the compensation means can be provided with a lever which by means of a power cylinder or otherwise operates on the shaft, particularly the bearings of the shaft. The lever and the shaft can in this case be connected by means of an elastic hinge-assembly. With a limited displacement of the power cylinder it is possible to work with quite a large mechanical transmission, since this hardly or never needs to move. The elastic hinges are extremely well-suited to this purpose. The invention will be explained using a drawing. Fig. 1 shows a schematic representation of a pulley according to the state of the art and provided with a drive belt; Fig. 2 shows a schematic representation in longitudinal section of a pair of pulleys according to one embodiment of the invention, and Fig. 3 shows a schematic representation of an embodiment of the compensation means. Figure 1 represents schematically a prior art pulley with discs 1 and 2. Drive belt 12 is taken up between the discs 1 and 2. The disc 1 is fixed on the pulley shaft 3, while the pulley disc 2 is fixed against rotation on, but is axially slidable along, shaft 3. In a known way, disc 2 is provided with an operating cylinder 30 with cylinder wall 4 and piston 6. By changing either the pressure in the cylinder or the discharge flow through the cylinder, as known, the axial position of disc 2 in relation to shaft 3 and disc 1 can be adjusted. The distance R of the drive belt from the centre line of shaft 3 is dependent on the momentaneous transmission ratio of, for example, a continuously variable transmission, in which the pulley/drive belt assembly is installed. It is however clear that the drive belt 12 is always situated radially outwards from shaft 3. In this case the drive belt 12 only makes contact with the discs 1, 2 over the circle segment Ψ. The distributed load exterted by the drive belt onto discs 1 and 2 produces a resultant force F on the discs 1, 2. The discs 1, 2 and especially shaft 3 will therefore deform somewhat. Due to the deformation, constant contact pressure between the discs 1, 2 and the drive belt 12 will not be achieved. The load on drive belt 12 will increase locally and the lifetime will decrease. Furthermore, in some cases, in order to compensate for the phenomenon, the pressure in the operating cylinder is increased, as a result of which the efficiency of the transmission decreases. In figure 2, a pair of pulleys with discs 21, 22 and 23, 24 are represented. The fixed discs 21 and 24 are mounted on shafts 25 and 26 respectively. The shafts 25 and 26 are provided with bearings 27 and 28 respectively, at the position of, and in this case partially enclosed by, the fixed discs 21 and 24 respectively. Moreover, the shafts 25 and 26 are provided with tail bearings 29 and 31. The bearings 27 and 29, and 28 and 31 respectively are incorporated into torsion-rigid bearing housings 32 and 33 respectively, which, for example, can again be incorporated into the housing and/or be mutually rigidly connected. Because of these measures, the fixed discs 21 and 24 are optimally mounted on and supported by the shafts 25 and 26 respectively, so that these discs undergo a minimal displacement and tilting. The two slidable discs 22, 23 comprise moreover operating cylinders 35 and 36 respectively, of which the pistons 37 and 38 respectively cooperate with the cylinder walls 39 and 40 respectively on the one side, and on the other side are fixed to the hollow shafts 41 and 42. The hollow shafts 41 and 42 are fixed on the thin extremities 25' and 26' respectively of the shafts 25 and 26 respectively, which in this case are made by the bolts fastened in the shafts 25 and 26 respectively. The bosses 43 and 44 of the discs 22 and 23 respectively are mounted on the shafts 25 and 26 respectively in both radial and tangential directions, also by means of the ball hinges 34, and are permanently connected with the shaft parts 45 and 46 respectively which are journalled in the hollow shafts 41 and 42 respectively. In this way, the discs 22 and 23 are connected with the thinner and therefore more flexible extremities 25' and 26' respectively of the shafts 25 and 26 respectively, as a result of which a suitable construction for power transmission and power compensation is obtained. The hollow shafts 41 and 42, fixed on the shaft extremities 25' and 26' are provided with bearings 47 and 48 respectively. The compensation means 49 and 50 respectively operate on these bearings 47 and 48, and exert a variable resultant radial force on the shafts 25 and 26 respectively. Because of this, a moment is exerted on the slidable discs 22 and 23 respectively. A resultant eccentric axially-directed force between the discs 21 and 22, and 23 and 24 respectively is the outcome. This eccentric force between the discs works together with the axial centric pressure of the operating cylinders 35 and 36 respectively, as a result of which the desired contact pressure for the drive belt between the discs is obtained. In addition to this, the invention can also be applied in combination with pressure means, among which operating cylinders which realize an axial eccentric contact pressure for the drive belt between the discs, such as is described for example in the American patent 5,013,283. Because a deformation of the discs 22 and 23 and the shafts 25 and 26 respectively, caused by drive belt 51, is dependent on the radial position of the drive belt 51 in the pulleys and/or the transmission ratio of a continuously variable transmission, the compensation means can yield a variable force according to size and position. This can for example be achieved with a power cylinder which for example, can be (hydraulically) connected, if required via a control system, to operating cylinders 35 and 36 respectively. The possible control system can in this case adjust the pressure as desired. An embodiment of the compensation means according to the invention is represented in figure 3. The compensation means comprise a lever 61 in which the bearing 47 is incorporated. The lever 61 with the pulling cylinder 62 exerts its action in a system of elastic hinges and levers, in this case, the said lever 61 and the lever 70. The lever 70 is connected to the housing by means of the leaf springs 65 and the block 68 and to the pulling cylinder 62, referred to as power cylinder in the claims, by means of the leaf spring 64. The lever 61 is connected to the housing 66 by means of the leaf spring 63 and the block 67. Moreover, an adjustment bolt 69 provides for such a fine adjustment of the compensation means that the shafts 25' and 26' respectively are either not bent or are hardly bent during operation. Because of this embodiment, a robust bearing is achieved, wherein with only a limited displacement of the pulling cylinder 62, an optimal resultant and variable force is achieved. It will be clear that the invention is not limited to the represented embodiment forms of the invention, but that within the framework of the invention, many more embodiments are conceivable that are considered to fall under the idea of this invention. By way of example, both discs of the pulley can be mounted on the shaft so that they can slide.

Claims: Pulley, in particular for a continuously variable transmission, provided with at least two discs (21, 22; 23, 24), which are primarily co-axially installed on a pulley shaft (25; 26) and are fixed against mutual rotation, wherein at least one of the discs (22; 23) is slidable in relation to the pulley shaft (25; 26) by means of displacement means (35; 36) and wherein compensation means (49; 50) are provided to exert a resultant eccentric, axially-directed force between the two discs (21, 22; 23, 24), characterized in that at least that part (25'; 26') of the pulley shaft (25; 26) lying between the point of application of the resultant force to be exerted by the compensation means (49; 50) and that disc that is nearest to said compensation means is made primarily relatively flexible. Pulley according to claim 1, characterized in that the relatively flexible part (25'; 26') of the pulley shaft is thinner than the basic part of the pulley shaft (25; 26). Pulley according to claim 1 or 2, characterized in that the slidable disc (22; 23) is at least partially mounted onto the relatively flexible part (25'; 26') of the pulley shaft. Pulley according to one of the preceding claims, characterized in that at least one of the two discs (21, 22; 23, 24) is supported on the pulley shaft by means of a hinge. Pulley according to claim 4, characterized in that the hinge comprises a ball hinge. Pulley according to one of the preceding claims, characterized in that the other disc (21; 24) of said at least two discs (21, 22; 23, 24) is fixed on the pulley shaft, and the pulley shaft facing away from the fixed disc (21; 24) is provided with at least two bearings (27, 29; 28, 31). Pulley according to claim 6, characterized in that a first bearing (27; 28) is installed at the position of the fixed disc (21; 24) and a second bearing (29; 31) is installed at a distance from said fixed disc. Pulley according to claim 7, characterized in that the first and the second bearing (27 and 29; 28 and 31) are connected by a torsion-rigid bearing housing (32; 33) that is securable. Pulley according to one of the claims 7 to 8, characterized in that the first bearing (27; 28) is at least partially enclosed by the fixed disc (21; 24). Pulley according to one of the preceding claims, character ized in that the compensation means are equipped to exert a variable resultant eccentric radially-directed force. Pulley according to one of the preceding claims, characterized in that the compensation means comprise a power cylinder (62). Pulley according to claim 11, characterized in that the displacement means comprise an operating cylinder (35; 36) and that the operating cylinder and the power cylinder (62) are mutually connected. Pulley according to claim 12, characterized in that the operating cylinder (35; 36) and the power cylinder (62) are connected by means of a control system. Pulley according to one of the claims 11, 12 or 13, characterized in that the power cylinder (62) operates on a bearing (47; 48) of the pulley shaft (25; 26). Pulley according to claim 14, characterized in that said bearing (47; 48) lies at a distance from the slidable disc (22; 23). Pulley according to one of the preceding claims, characterized in that the compensation means comprise at least one lever. Pulley according to claim 16, characterized in that said power cylinder (62) operates on said at least one lever. Pulley according to claim 16 or 17, characterized in that said bearing (47; 48) is connected to said at least one lever. Pulley according to one of the preceding claims, characterized in that the compensation means comprise an elastic hinge assembly. Pulley according to claim 19, characterized in that the power cylinder (62) and said at least one lever are connected by means of elastic hinges and said at least one lever operates on the pulley shaft. Pulley according to one of the preceding claims, characterized in that said slidable disc is provided with pressure means for a centrical or eccentric axial pushing of the disc.

Inventors: LAMERS GERARDUS JOHANNES MARIA, VAN SPIJK JOHANNES GERARDUS LU, LAMERS, GERARDUS JOHANNES MARIA, VAN SPIJK, JOHANNES GERARDUS LUDOVICUS
Applicants: DOORNES TRANSMISSIE BV, VAN DOORNE'S TRANSMISSIE B.V.
Application year: 1994
Main classification: F16H55
IPC codes: F16H61, F16H55, F16H9